Holy old thread... but I have had the same experience. Right side brake light error, one of the 921/W16Ws on that side was still working but very blackened, I replaced only that bulb and no more errors.

The only other bulb error I've had on the car was one of the angel eyes, and that one was burned out. Looking at the service history of the car though it looks like the dealership replaced a lot of light bulbs on the car.